(1) Field of the Invention
This invention relates a process for producing a polymeric layer having a desired image thereon and to a process for forming three-dimensional articles having selectively coloured regions, formed from a plurality of the aforementioned polymeric layers.
(2) Description of Related Prior Art
A photopolymerisable composition containing crystal violet lactone and the photoinitiator called Lucirin TPO is known from European patent application No.251,049. The compositions were apparently used to produce a photoresist layer by applying them to a substrate, irradiating desired areas to form a polymer coating in the irradiated areas, then rinsing to remove areas which had not been irradiated.
A method for producing three-dimensional articles called `stereolithography` is also known. This method comprises curing successive layers of a photopolymerisable liquid using a computer-controlled light source, e.g. a laser, and cohesively integrating the layers to give the desired article. Stereolithography has been used to prepare mechanical parts for cars, prosthetic devices, medical models and a variety of other articles having complex internal structures. Hull's U.S. Pat. No. 4,575,330, U.S. Pat. No. 4,752,498 and Hideo Kodama's article in Rev. Sci. Instrum. 52 (11), 1770-1773, Nov. 1981 describe this method in more detail.
Zeneca's international patent application No. PCT/GB94/01427 describes a stereolithography method for forming a three-dimensional article having at least one selectively coloured region from a photopolymerisable, photocolourable composition containing an infra-red absorber. In this process layers of the composition are cured by light of a wavelength outside the infra-red, e.g. UV light, and coloured by a beam of infra-red light.